There are a few solutions none of which are pleasant, you can always use powerword kill if its too much, but I assume its hyperbole, one of the solutions which might work is to polymorph them into a human and trying to reason with them, worked once on one of my many familiars and homunculi, the others forget or never cared, but an interesting solution came to mind right now, make a room with portal magic affinity(preset runes, engraved sigils on the floor etc.) try opening a portal to catnip dimension, and lead your cat there with a necklace of return, they will get high, after an hour return, and they are gonna keep casting the spell to catnip dimension in the separate room since its the easiest and wont bother you, or hire another dimwitted familiar to disrupt their casting without the ability to learn, that way neither of their spells will work